1. Field of the Invention
The present invention relates to an intermediate transfer belt and a producing method of the intermediate transfer belt, and an image forming apparatus.
2. Description of the Related Art
Conventionally, in an electrophotographic image forming apparatus, an endless belt (seamless belt) has been used as a member in a variety of applications. Particularly, in full-color image forming apparatuses of recent years, an intermediate transfer belt system is used, in which developed images of four colors: yellow, magenta, cyan and black, are superposed on an intermediate transfer belt and then the superposed image is collectively transferred to a recording medium such as paper.
However, in such an intermediate transfer belt system, four developing devices are used for one photoconductor. Such an intermediate transfer belt system has a disadvantage that printing speed is low. For a system capable of attaining high speed printing, a four-series tandem system is used in which photoconductors for four colors are arranged in a tandem manner, and each color is continuously transferred on paper.
However, in this four-series tandem system, it is quite difficult to achieve sufficient positional accuracy upon superposing respective images because of changes of conditions of paper due to the working environments, forming images where the color images are not accurately superposed on top of each other.
Thus, recently, an intermediate transfer system has been predominately applied in the four-series tandem system.
Under such circumstances, characteristics required for the intermediate transfer belt have become strict to achieve, such as positional accuracy or high-speed transfer, but it is necessary to satisfy those characteristics.
The intermediate transfer belt has a primary transfer function of receiving a toner from an image bearing member and a secondary transfer function of delivering the toner to paper, in both of which transfer rate is needed to be improved. Especially, when the transfer rate is low in the secondary transfer, residual toner which has not transferred to paper remains on the intermediate transfer belt, which tends to cause image failure or filming.
In recent years, full-color electrophotographic image formation has increasingly been performed on various types of paper, such as commonly-used smooth paper, highly-smooth papers with slip properties (e.g., coated papers) and rough paper (e.g., recycled paper, embossed paper, Japanese paper and kraft paper). Generally, the secondary transfer rate in the case of printing to rough paper tends to be lower than that of to plain paper. This is because the intermediate transfer belt cannot completely contact with recessed portions on rough paper, so that toner may be insufficiently transferred to paper and remain on the intermediate transfer belt. In order to improve the followability to rough paper, various intermediate transfer belts have been proposed which include a base layer and a relatively flexible elastic layer laminated on the base layer.
Generally, the elastic layer contains elastic materials such as rubber or elastomer. However, there has been an attempt to use softer rubber for the elastic layer in order to improve transferability to rough paper.
When the intermediate transfer belt having the elastic layer which contains the softer rubber is produced and stored, a fatty acid such as stearic acid added as lubricant for improving processability at a kneading step of rubber may bloom onto the intermediate transfer belt over time (blooming). Especially, it has been known that the blooming easily occurs after storing under a high temperature and high humidity environment for a long period, followed by under a low temperature environment. When a fatty acid bloomed from the intermediate transfer belt adheres to an image bearing member, the image bearing member degenerates to thereby deteriorate image quality, which is problematic.
In order to solve the above problem, there have been conducted various studies regarding a method for preventing a fatty acid from blooming on the intermediate transfer belt. For example, there has been proposed a method in which a surface layer is formed on an elastic layer (see Japanese Patent Application Laid-Open (JP-A) Nos. 2006-091497 and 2004-198713).
However, in the above proposition, in the case where rubber hardness of the elastic layer is low, the surface layer is cracked or crinkled when the surface layer having relatively high hardness is formed on the elastic layer, which is problematic.
Meanwhile, when a surface layer having high flexibility is formed on a soft elastic layer, a surface of an intermediate transfer belt is deteriorated in releasability, so that toner cannot be efficiently released from the surface and the transfer rate of the toner from the intermediate transfer belt to paper tends to be lowered.
Accordingly, there is a need for providing an intermediate transfer belt which can prevent a fatty acid from blooming over time regardless of storage environment of the intermediate transfer belt, which allows a stable transfer for a long period, and which can achieve high-quality images.